When a silicon film is formed on a substrate, as a source gas, a gas containing silicon, chlorine, and hydrogen, for example, dichlorosilane (SiH2Cl2) is supplied to the reaction chamber. After the silicon film is formed, an exhaust gas exhausted from the reaction chamber contains an unreacted source gas. Therefore, as a byproduct derived from the exhaust gas, a liquid chlorosilane polymer or the like is attached to an exhaust pipe connected to the reaction chamber. The chlorosilane polymer is also referred to as an oily silane.
Since the chlorosilane polymer has a high viscosity, if the chlorosilane polymer is left as it is, the exhaust pipe is clogged, so that there is a problem in that trouble occurs in the formation of the silicon film. In addition, since the chlorosilane polymer has ignitability, the removal process is accompanied with a risk. For this reason, there is a problem in that the removal process of the chlorosilane polymer takes time and effort.